The two decisions make it easier to challenge even the appearance of racial bias in the jury selection process, analysts say. The decisions also send a message to trial and appeals-court judges that they must be more attentive to allegations of racial inequality in jury selection and take more aggressive steps to investigate bias allegations.

"Decisions about who should live or die or who should serve on a jury should not be influenced by race," says Richard Dieter, executive director of the Death Penalty Information Center.

In Jay Shawn Johnson v. California, the high court struck down a portion of California's test for racial bias in jury selection. The justices said California's test made it too hard for some challengers to get beyond an initial showing to obtain an inquiry by the trial judge. The vote was 8 to 1.

In Thomas Miller-El v. Doug Dretke, the Supreme Court ordered a new trial for Mr.

Miller-El, a black death-row inmate in Texas, because of allegations that prosecutors improperly excused black jurors from the jury panel that sentenced him to die in 1985. Prosecutors said race did not play a role in their decision to excuse 10 of 11 black jurors from the panel. Trial and appeals-courts judges agreed with this assessment.

On Monday, the nation's highest court reversed, saying that the Texas court's conclusion "was unreasonable as well as erroneous." The 6-to-3 majority opinion was written by Justice David Souter.

"It is true, of course, that at some points the significance of Miller-El's evidence is open to judgment calls, but when this evidence ... is viewed cumulatively its direction is too powerful to conclude anything but discrimination," he writes.

In a dissent joined by Chief Justice William Rehnquist and Justice Antonin Scalia, Justice Clarence Thomas says much of the evidence relied upon by the high court had not been heard in the Texas courts.

"For nearly 20 years now, Miller-El has contended that prosecutors peremptorily struck potential jurors on the basis of race," Justice Thomas writes. "In that time, seven state and six federal judges have reviewed the evidence and found no error. This court concludes otherwise, because it relies on evidence never presented to the Texas state courts."

Miller-El was convicted and sentenced to die for killing a Holiday Inn clerk during a robbery. During selection of his jury, 10 of 11 blacks (91 percent) were excluded under peremptory challenges by prosecutors. "The prosecutors' chosen race-neutral reasons for the strikes do not hold up and are so far at odds with the evidence that pretext is the fair conclusion," Souter writes.

He adds that the two prosecutors in the case had been trained in how best to exclude blacks from cases as part of a strategy to help convict black defendants. He writes that they used race-coded juror cards, requested random shuffles of the jury pool, and engaged in disparate questioning designed to knock blacks off the panel while allowing whites to continue as jury members.

The jury selection process involves two ways that prospective jurors may be disqualified from service. First, jurors may be dismissed "for cause," meaning there is a legitimate reason they should not sit on that particular jury. For example, if a prospective juror was a friend or neighbor of the victim, that person would automatically be excused from the jury pool.

The second way jurors may be disqualified is through peremptory challenges. In each jury trial, the judge awards both sides a number of peremptory challenges. In effect, each is a free pass to kick anyone off the jury for any reason, except race. The Supreme Court declared in a 1986 case called Batson v. Kentucky that race may not be a factor in jury selection.

But policing that command has been difficult. Because of the murky nature of jury selection strategy and the potentially wide range of reasons behind any particular peremptory challenge, it is often hard to show an improper racial motive.

"This is a turning point in review of Batson claims," says Bernard Harcourt, a law professor at the University of Chicago Law School. "It suggests greater federal review of state decisions."

In Johnson v. California, the high court overturned a state Supreme Court decision upholding a higher standard of proof in cases of alleged bias in jury selection.

Mr. Johnson, who is black, was convicted by an all-white jury of second-degree murder in the killing of the 19-month-old daughter of his girlfriend, who is white. There had been three African-Americans in the initial jury panel, but all three were dismissed through the use of peremptory challenges by the prosecutor.

Johnson's lawyer filed an objection to the dismissal of the three black prospective jurors. He asked the trial judge to require the prosecutor to explain why the three had been dismissed. The trial judge declined to require a response from the prosecutor. Nonetheless, the judge found that nonracial reasons existed to justify the exclusion of the three prospective jurors under peremptory challenges.

Johnson appealed his conviction on grounds that his jury was tainted by unconstitutional racial discrimination that forced blacks off his jury panel. A California appellate court agreed and reversed his conviction.

But the California Supreme Court reinstated the conviction, saying Johnson's lawyer had failed to present enough evidence of racial bias by the prosecutor.

At the center of the case was the issue of how much evidence is enough to trigger a three-part inquiry into alleged racial bias.

"The court did not intend the first step to be so onerous," writes Justice John Paul Stevens for the majority. "A defendant satisfies Batson's first step requirements by producing evidence sufficient to permit the trial judge to draw an inference that discrimination has occurred."

He adds, "California's standard is at odds with the ... inquiry mandated by Batson."

In a lone dissent in the California case, Thomas says the court afforded states flexibility in complying with the dictates of the Batson decision. "California's procedure falls comfortably within its broad discretion to craft its own rules of criminal procedure," he says.